The effects of sodicity on seedling emergence, ion uptake, growth, survival and yield of hexaploid wheat varieties and tetraploid wheat genotypes were investigated. For this study a series of pot experiments was conducted under glasshouse and growth room conditions at the Henfaes Agriculture Research Station, University of Wales, Bangor, UK. Sodicity was artificially created by treating soils with NaHCO3• The relative effects of poor soil structure and
high ESP were investigated by treating soil with NaHCO3 and by stabilising soil aggregates with an anionic polyacrylamide (PAM) soil conditioner. Comparison of the effects of salinity and sodicity was investigated by adding a mixture of NaCl, CaCli and MgCli salts into the soil. The effects of sodicity at different growth stages were investigated in experiments with seedlings and
mature plants and in experiments conducted by transplanting wheat seedlings into sodic soil.
The results of this study revealed that, with the exception of seedling emergence, the adverse effects of sodicity were higher than those of salinity. The effects of sodicity increased with increase in exchangeable sodium percentage (ESP) of the soil, and were generally more pronounced in clay loam and loamy sand soils with low organic matter and N %. The adverse effects of salinity were associated with high Na+ and er, low K+/Na+ ratio in leaf sap and osmotic effects, possibly reflected by high ECe, The adverse effects of sodicity were associated with high
Na+, low K+, Ca2+ and lower K+/Na+ ratio in leaf sap, grain and straw dry matter, but not with decreased concentrations or toxic levels of micronutrients. The large effects of sodicity were related directly with high ESP and pH and indirectly with poor soil structure (low water stable aggregates%).
Addition of PAM to sodic soils resulted in large increases in the water stable aggregates (WSA % ), which in turn increased seedling emergence %, survival %, shoot height, shoot dry weight, grain yield and almost all yield components in sodic soils. Addition of PAM also increased K+ and K+/Na+ ratio and decreased Na+ in leaf sap, grains and straw dry matter.
Wheat plants transplanted into sodic soil survived and produced ears, but the surviving plants did not produce grains at high ESP. Transplantation of 16 and 21 day old seedlings generally resulted in higher grain and straw yield than the sowing of dry and pre-germinated seeds in sodic soils with ESP below 40. The improved performance of transplanted seedlings in sodic soils was not clearly associated with changes in ion concentrations in flag leaf sap.
There were differences between wheat varieties and genotypes in terms of how they were affected by sodicity, and how they performed in sodic soil treated with PAM. Kharchia-65, a hexaploid wheat variety, and Rl 12+ and Rl 73+, tetraploid wheat genotypes which posses a gene (Knal) which enables them to discriminate between K+ and Na+, were generally tolerant to both sodicity as well as salinity from seedling stage to maturity. The improved growth and yield of most of the varieties and genotypes in the PAM treated sodic soils . was generally associated with lower leaf Na+ and higher K+ and K+/Na+ ratio, but not with increased concentrations of micronutrients.
These results suggest that substantial improvement in the performance of wheat in sodic soils can be quickly achieved by adding PAM. These results also indicate that the primary cause of low wheat yield in sodic soils with ESP up to 40 or 50 may be poor soil structure and that the decrease in yield due to ion toxicity is relatively small. In sodic soils with ESP above this range 40 to 50 the major cause of low yield may be high exchangeable Na+ and the effect of improved structure is relatively smaller. The results from this study support the use of PAM in sodic soils and selection of varieties such as Kharchia-65 and genotypes Rl 12+ and R73+ for use in future breeding programmes to screen out new local genotypes that can tolerate poor soil structure as well as salts.